Finger medical sensor

ABSTRACT

The present invention relates to a medical sensor ( 1 ) for measuring pulse, blood, tissue and/or skin parameters using electromagnetic waves in the transmission method, comprising a carrier part ( 2 ) for pushing onto a patient&#39;s finger or toe. A first carrier leg ( 12 ) carries a transmitter unit ( 5 ) and a second carrier leg ( 13 ) carries a receiver unit ( 6 ). A carrier base ( 14 ) connects the two carrier legs ( 12, 13 ) to one another in the region of a tip of the finger or toe. A spring part ( 3 ) is arranged on the outside of the carrier part ( 2 ) such that a first spring leg ( 15 ) bears against the first carrier leg ( 12 ) and a second spring leg ( 16 bear against the second carrier leg ( 13 ). The carrier part ( 2 ) is made of a more flexible material than the spring part ( 3 ), in which the spring legs ( 15, 16 ) prestress the carrier legs ( 12, 13 ) toward one another.

The present invention relates to a medical sensor for measuring pulse,blood, tissue and/or skin parameters using electromagnetic waves in thetransmission method.

During an operation or during a stay in intensive care, it may beexpedient to check and monitor inter alia the lung function, metabolismand heart rate of the patient. This may be carried out, for example, bymeasuring the oxygen saturation and the pulse rate. Sensors of the typementioned above are used for this, and these can be used to carry out ameasurement, derived from the pulse, of the arterial oxygen saturationby means of an optoelectronic transmission measurement. Such a sensoroften includes at least one transmitter, for example a light-emittingdiode, or LED for short, with infrared light and an LED with red light,and also at least one receiver, usually a photodiode, and a carrierassembly which positions the transmitter and the receiver in the desiredmanner on a finger or toe of the patient.

With these sensors, a distinction is made between single-use sensors,semi-reusable sensors and reusable sensors.

In patients of different size, the diameter of the fingers and toes isconsiderably different. Accordingly, the patients are divided up intogroups in terms of their size, for example large adult, adult, smalladult and child.

A sensor that is designed as an adhesive sensor is known from EP 0 127947 B1, in which the carrier component consists essentially of anadhesive tape which is wound around the finger or toe and stuck thereto.Although such adhesive sensors are designed as disposable sensors, theyare relatively expensive on account of their complex manufacture. Inorder to obtain correct measurement results, the adhesive sensors mustbe positioned carefully depending on the size of the respective fingerand/or toe. In order to simplify or allow attachment of the adhesivesensors to patients of different size, the adhesive sensors are usuallyavailable in different sizes.

Sensors designed as clip sensors, which in each case have two legsmounted on one another in a manner such that they can pivot about apivot spindle, are known from U.S. Pat. No. 3,810,460 and U.S. Pat. No.4,685,464. One of the legs contains the transmitter while the other legcontains the receiver. In the known clip sensors, the transmissiondirection of the transmitter and the receiving direction of the receiverchange as a function of the pivot angle between the clip legs. The knownclip sensors may therefore supply reliable measurement results onlywithin predefined, relatively narrow angle ranges. Accordingly, the clipsensors must be provided in various sizes for patients of differentsize. In addition, at large opening widths, the pressure on the fingeror toe that is generated by the clamping legs becomes so great that itobstructs the blood supply and falsifies the measurement. The clipsensors are constructed in a relatively complex manner and may thereforeonly be provided as reusable sensors.

Other sensors which are designed as sleeve sensors are known from DE 3703 458 C2 and U.S. Pat. No. 4,109,643. In sleeve sensors, the carriercomponent is designed as a sleeve which can be pushed onto the finger ortoe and then surrounds the latter on all sides. However, the openingwidth of the sleeves can be changed only to a relatively limited extent.In the case of relatively large fingers or toes, the pressure becomes sogreat that the blood flow in the finger or toe is obstructed. In thecase of relatively small fingers or toes, the contact with the surfacemay be lost, so that in this case too no measurements are possible.Furthermore, these sleeve sensors are constructed in a relativelycomplex manner, so that they are expensive to manufacture and are usedonly as reusable sensors.

A common feature of the known sensors is that they are suitable only asreusable sensors on account of their complex design and/or to achieve asufficiently high functional reliability must be provided in varioussizes in order to be able to carry out the desired measurements onpatients of different size.

The object of the present invention is to specify an improved embodimentfor a medical sensor of the type mentioned in the introduction, whichmakes it possible in particular to carry out the necessary measurementson a number of, preferably all, conventional patients with one sensorsize. Furthermore, it should be possible to manufacture the sensor insuch an economical manner that is can be provided as a disposablesensor.

This object is achieved according to the invention by the subject matterof the independent claim. Advantageous embodiments form the subjectmatter of the dependent claims.

The invention is based on the general concept of equipping the sensorwith a clip-like flexible carrier part and a likewise clip-like, butmore rigid, spring part, where the relatively flexible carrier partcarries the transmitter and the receiver on opposite carrier legs whilethe relatively hard spring part prestresses the carrier legs toward oneanother by virtue of opposite spring legs. By means of the proposeddesign, the functions “holding and positioning of the transmitter andreceiver” and “retaining of the sensor on the finger or toe” aredistinct from one another and assigned to different components. As aresult, it is possible to optimize the various components in relation totheir function. According to the invention, the carrier part is designedto be more flexible than the spring part, as a result of which thecarrier part can adapt better to the finger or toe that is inserted ineach case. By contrast, by means of a spring force the spring partgenerates the necessary retaining forces to keep the sensor on therespectively inserted finger or toe.

The sensor according to the invention in principle operates like a clipsensor but does not require a positioning spindle and can accordingly bemanufactured in an economical manner. By configuring the carrier partand the spring part with in each case two legs which are connected toone another by a base, the sensor can be dimensioned relatively simplyin a manner such that it can be used for a relatively large finger ortoe diameter range.

A particularly economical manufacture results when the carrier part ismade in one piece and/or when the spring part is made in one piece.Carrier part and/or spring part may then be manufactured in largenumbers economically, as a result of which the manufacturing costs forthe sensor are considerably reduced.

One embodiment in which the spring part has at least one spring zonewhich connects together two support sections that adjoin it, saidsupport sections being more rigid than the spring zone, is particularlyadvantageous. By means of this design, the spring characteristic of thespring part can be deliberately configured such that there are restoringforces that are adapted to the opening widths.

When the spring part has two or more spring zones, it may beadvantageous for these to be configured with different rigidities. Thismeasure also simplifies the adaptation of the spring characteristic ofthe sensor to the requirements of different finger or toe diameters.

An embodiment in which the support sections which adjoin the moreflexible spring zone form a stop which restricts the bending deformationin this spring zone to a predefined extent during widening of thecarrier legs is of particular interest. On account of this design, bymeans of the stop in the spring characteristic of the sensor, a step isrealized in which the rigidity of the spring part changes in the mannerof a jump. On account of this design, the adaptation of the restoringforces to the requirements of differently sized fingers or toes isimproved.

A further important embodiment is characterized in that on the outsideof the carrier part there is a groove which extends from the outer sideof the first carrier leg via an outer side of the carrier base to theouter side of the second carrier leg, in which the at least onetransmitting element and the at least one receiving element are arrangedand in which connection cables for the transmitting element and thereceiving element are laid, wherein the spring part closes this groovefrom outside. In this design, the optoelectronic components and theircables can be accommodated in the carrier part in a relatively simplemanner. The secure holding thereof on the carrier part is then ensuredby the fitted spring part, as a result of which the spring part is givenan additional function. The assembly of the sensor is simplifiedthereby.

Further important features and advantages of the invention emerge fromthe dependent claims, the drawings and the associated description of thefigures with reference to the drawings;

It will be understood that the features which have been mentioned aboveand are yet to be mentioned below can be used not only in thecombination respectively specified but also in other combinations oralone without departing from the scope of the present invention.

The invention will be further described with reference to examples ofembodiments shown in the drawings to which, however, the invention isnot restricted. The same references relate to identical or functionallyidentical or similar components.

FIG. 1 shows a perspective view of the individual parts of a sensoraccording to the invention.

FIG. 2 shows a longitudinal section through a carrier part of the sensoron section line II in FIG. 3.

FIG. 3 shows a view of the carrier part from the front.

FIG. 4 shows a view of the carrier part from behind.

FIG. 5 shows a view of the carrier part from above.

FIG. 6 shows a view of the carrier part from below.

FIG. 7 shows a longitudinal section as in FIG. 2, but through a springpart of the sensor.

As shown in FIG. 1, a medical sensor 1 according to the inventioncomprises a carrier part 2, a spring part 3 and a signal transmissionunit 4. In addition, a fixing strip or fixing tape 48 may be provided.The sensor 1 is used to measure pulse, blood, tissue and/or skinparameters on a finger or toe of a patient. The sensor 1 is additionallyused for measuring the oxygen saturation, with it being possible for thepulse rate to be determined at the same time. The sensor 1 operatesusing electromagnetic waves, preferably with visible and/or invisiblelight. The sensor 1 operates according to the transmission principle, inwhich the electromagnetic waves of at least one transmitting element areirradiated into the finger or toe and the waves emerging from the fingeror toe on the opposite side are measured and evaluated by means of atleast one receiving element.

For this purpose, the signal transmission unit 4 comprises a transmitterunit 5 comprising at least one transmitting element that is notdiscussed in any more detail here. Such a transmitting element may beformed for example of an LED. The signal transmission unit 4 furthercomprises a receiver unit 6 which comprises at least one receivingelement that is not discussed in any more detail here. Such a receivingelement may be for example a photodiode. The transmitter unit 5 or itstransmitting elements and the receiver unit 6 or its receiving elementsare connected to a plug 9 of the signal transmission unit 4 via firstcables 7 and second cables 8, respectively. The individual second cables8 of the receiver unit 6 are in this case combined to form a collectivecable 10. The collective cable 10 and the individual first cables 7 ofthe transmitter unit 5 are combined to form a common cable 11 whichleads to the plug 9.

The carrier part 2 is designed in the manner of a clip and accordinglyhas two carrier legs which lie opposite one another, namely a firstcarrier leg 12 and a second carrier leg 13. In FIG. 1, the two carrierlegs 12, 13 are connected to one another on a side remote from theobserver by a carrier base 14. In the preferred embodiment shown here,the carrier part 2 is produced as one piece. The carrier part 2 is madeof a relatively soft, elastically deformable material. The shaping ofthe carrier part 2 or of its carrier legs 12, 13 is selected such thatthe carrier part 2 can be pushed onto the patient's finger or toe fromthe front. The carrier base 14 is then located in the region of a tip ofthe finger or toe during the measurement operation.

The spring part 3 has essentially the same contour as the carrier part2. Specifically, the spring part 3 is likewise designed in the manner ofa clip and accordingly has two spring legs, namely a first spring leg 15and a second spring leg 16. The spring legs 15, 16 are also connected toone another on one side by a spring base 17. The spring part 3 ispreferably also produced in one piece, but is made of a relatively hard,elastically deformable material. The terms “relatively soft” and“relatively hard” relate to the relations between the carrier part 2 andthe spring part 3.

As shown in FIGS. 2 to 6, the carrier legs 12, 13 are in each casecurved concavely toward one another on inner sides 18, 19 that face oneanother. Accordingly, each carrier leg 12 has two laterally outwardlylying side cheeks 20 and 21 which in each case project from a centralzone 22 or 23 toward the respectively opposite carrier leg 12, 13. Ascan be seen from FIG. 3, the side cheeks 20 of the first carrier leg 12and the side cheeks 21 of the second carrier leg 13 are in alignmentwith one another, so that the carrier legs 12, 13 make contact with oneanother at their side cheeks 20, 21 in an initial state in which theyare pressed together to a maximum extent.

The carrier part 2 on the outside contains a groove 24 which extendsfrom an outer side 25 of the first carrier leg 12 via an outer side 26of the carrier base 14 to an outer side 27 of the second carrier leg 13.In the first carrier leg 12, the groove 24 forms a first recess 28 foraccommodating the transmitter unit 5. In the second carrier leg 13, thegroove 24 forms a second recess 29 for accommodating the receiver unit6. Between the two recesses 28, 29, the groove 24 forms a cable channel30 in which the second cables 8 or the collective cable 10 can be laid.The first carrier leg 12 contains a further cable channel 31 which leadsfrom a front side of the first carrier leg 12 that is remote from thecarrier base 14 to the recess 28. In this further cable channel 31 theremay be laid an end section 32 (cf. FIG. 1) of the common cable 11. Thefirst recess 28 contains a transmission opening 33 through which the atleast one transmitting element can irradiate the electromagnetic wavesto the receiver unit 6. In a corresponding manner, the second recess 29contains a receiving opening 34 through which the at least one receivingelement can receive the waves emitted by the transmitter unit 5.

To assemble the sensor 1, the end section 32 of the common cable 11 isintroduced into the further cable channel 21 and expediently fixedtherein, for example by clamping or adhesive bonding. The transmitterunit 5 is inserted into the first recess 28 and expediently fixedtherein, e.g. by adhesive bonding. Furthermore, the receiver unit 6 isinserted into the second recess 29 and expediently fixed therein, e.g.by adhesive bonding. The collective cable 11 is laid in the cablechannel 30. The spring part 3 is then placed on the outside of thecarrier part 2. The spring part 3 serves as a closure or cover for thegroove 24. This means that the assembled spring part 3 covers or closesthe recesses 28, 29 and the cable channels 30, 31. The spring part 3 isalso expediently fixed in a suitable manner on the carrier part 2, forexample by welding. On the outside, the carrier part 2 has a receivingcontour 35 that is adapted to the contour of the spring part 3. Thespring part 3 is thereby at least partly sunk into the outside of thecarrier part 2 and laterally fixed by the receiving contour 35.

In FIGS. 2 to 6, the spring part 3 attached to the carrier part 2 isshown by broken lines.

As shown in FIG. 7, the clip-like spring part 3 is also expedientlyproduced as one piece. In this case, the spring part 3 is made of amaterial that is elastically, in particularly spring-elastically,deformable but has a greater rigidity than the material of the carrierpart 2. Compared to the carrier part 2, the spring part 3 is thus madeof a hard material.

The spring part 3 has at least one spring zone, in this case two springzones, namely a first spring zone 36 and a second spring zone 37. Eachspring zone 36 and 37 connects together two support sections 39 of thespring part 3 which adjoin it. Specifically, the first spring zone 36connects a first support section 39 a to a second support section 39 b,while the second spring zone 37 connects the second support section 39 bto a third support section 39 c. The configuration of the spring zones36, 37 is selected such that the spring zones 36, 37 are in each casemore flexible than the adjacent support sections 39. This means that thesupport sections 39 are more rigid than the spring zones 36, 37 arrangedtherebetween.

In the preferred embodiment shown here, the first spring zone 36 is madeat a transition 40 between the second spring leg 16 and the spring base17. The first spring zone 36 is in this case formed by a materialcontraction, as a result of which the first spring zone 36 has acomparatively low spring elasticity.

The second spring zone 37 is in this case made approximately in themiddle of the spring base 17. The second spring zone 37 is realized by aflattening 44 which reduces the wall thickness of the spring base 17 inthe region of the second spring zone 37. The second spring zone 37 isconfigured such that its rigidity is greater than that of the firstspring zone 36.

The first spring leg 15 in this case comprises two sections, namely anend section 42 and a start section 43. While the start section 43directly adjoins the spring base 17, the end section 42 is remote fromthe spring base 17. The two sections 42, 43 are differentiated from oneanother in that the end section 42 is more flexible than the startsection 43. This is achieved in this instance by different materialthicknesses. As can be seen from FIG. 7, the end section 42 adjoins thestart section 43 in a region 38. This region 38 is positioned along thefirst spring leg 15 in a manner such that it is arranged approximatelyin the center with respect to the second spring leg 16. Usually, then,this region 38 is located in a position in which a fingernail or toenailend that is remote from the finger tip or toe tip of the finger or toeinserted in the sensor 1 is located. The transition between the twosections 42, 43 is in this case formed by a step 41 in the region 38.The spring elasticity of the end section 42 is expediently matched tothe spring elasticities of the first spring zone 36 and of the secondspring zone 37. The end section 42 is expediently more rigid than thesecond spring zone 37. The two spring zones 36, 37 and the relativelyflexible end section 42 form three preferred bending zones within thespring part 3, which bending zones deform elastically to a greaterextent than the adjoining support sections 39 a, 39 b, 39 c duringwidening of the spring legs 15, 16.

The sensor 1 according to the invention operates as follows:

In an initial position, that is to say before the sensor 1 is pushedonto a finger or toe, the spring part 3 causes the sensor 1 or thecarrier part 2 to assume an initial state. In the assembled sensor 1,the spring legs 15, 16 bear against the outer sides 25 and 27 of thecarrier legs 12, 13 and stress them in the direction of one another. Thespring part 3 is designed such that it causes the carrier legs 12, 13 tobear against one another at their side cheeks 20, 21 in the initialstate. The sensor 1 may expediently be dimensioned such that it can bepushed onto the finger or toe of a child in such a manner that the twocarrier legs 12, 13 lift off one another. It is thus ensured that adesired application force for the carrier legs 12, 13 against the fingeror toe can be achieved even in the case of small fingers or toes. Whenthe carrier legs 12, 13 are widened, the first spring zone 36 isinitially deformed to the greatest extent. The resulting restoringforces are relatively small. Thus even in the case of children whonormally have a lower blood pressure than adults the restoring forcedoes not lead to any disruptive influencing of the blood flow and pulse.Nevertheless, the restoring forces generate a sufficient pressure to fixthe sensor 1 sufficiently on the finger or toe.

When the sensor 1 is attached to a larger child or to a small adult, thesecond carrier leg 13 can pivot out to a wide enough extent, with therestoring forces accordingly increasing the spring characteristic of thespring part 3.

In the case of an average-sized adult, the bending deformation of thefirst bending zone 36 reaches a predetermined value during widening ofthe carrier legs 12, 13, said predetermined value being delimited ordefined by a stop 45 in the specific embodiment of the spring part 3shown here in FIG. 7. This stop 45 is formed by flanks of the supportsections 39 a, 39 b which adjoin the first spring zone 36, these flankscoming to bear against one another when the predetermined bendingdeformation is reached, thus preventing further bending deformation inthe first spring zone 36. By means of this special design, the springcharacteristic of the spring part 3 at this point exhibits a jump. Thisis because, while below this limit bending deformation there is almost aserial connection of the rigidities of the three bending zones 36, 37,42, above said bending deformation there is only a serial connection ofthe rigidities of the second spring zone 37 and of the end section 42.This means that during bending of the carrier legs 12, 13, the restoringforces increase to a lesser extent up until the predetermined bendingdeformation is reached than in the case of a more extensive widening ofthe carrier legs 12, 13. Such a more extensive widening is achieved whenthe sensor 1 is used on a normal adult or on a large adult. In thosecases, greater restoring forces are also required in order to be able toobtain correct measurement results.

In the case of large adults, the bending deformation in the secondspring zone 37 may also reach a limit value, in which the springelasticity of the second spring zone 37 increases greatly on account ofthe design. Consequently, further widenings of the carrier legs 12, 13essentially act on the end section 42. This means that the springcharacteristic of the spring part 3 also exhibits a second step in whichthe rigidity of the spring part 3 changes once more.

On account of the shaping of the carrier part 2, during bending of thecarrier legs 12, 13 there are only relatively slight changes in thealignment of the transmitter unit 5 with respect to the receiver unit 6,so that a sufficient functional reliability can be ensured for themeasurements that are to be carried out, for a very large opening widthrange of the carrier legs 12, 13.

By virtue of the clip-like configuration of the carrier part 2, thecarrier legs 12, 13 come to bear flatly against an upper side and alower side of the respective finger or toe opposite one another at theirinner sides 18, 19. The side cheeks 20, 21 bring about centering of thefinger or toe, as a result of which the sensor 1 has an increasedlateral retention. Between the carrier legs 12, 13, the sensor 1 is openat the sides, as a result of which the build-up of sweat on the fingeror toe is reduced. The shaping of the carrier part 2 is moreoverselected such that the insertion depth for the finger or toe is limited.This is achieved in that the second carrier leg 13 forms an upward ramp46 at its section adjoining the carrier base 14, on which ramp the tipof the finger or toe comes to bear when the optimal penetration depth isreached. In the preferred embodiment shown here, the carrier base 14 isconfigured in a U shape in longitudinal section, as shown in FIG. 2, asa result of which the carrier base 14 forms a hollow 47. In patients whohave relatively long fingernails or toenails, this hollow 47 serves toaccommodate the respective fingernail or toenail if the latter projectsbeyond the tip of the finger or toe. The measurement is therefore notimpaired by relatively long fingernails or toenails.

Once the sensor 1 has been pushed onto the finger or toe of the patient,the sensor 1 is in principle sufficiently fixed on the finger or toe bythe restoring force of the spring part 3, in order to be able to carryout the respective measurements in the correct manner. In order to avoidposition changes of the sensor 1 relative to the finger or toe onaccount of voluntary or involuntary movements of the patient, additionalfixing measures may be provided to secure the sensor 1 to the finger ortoe. For example, for this purpose it is possible to use the fixing tape48 shown in FIG. 1, which after the sensor 1 has been pushed on is woundaround the finger or toe for example in the region of the end section 42of the first spring leg 15 and thus surrounds the sensor 1. In a morecomfortable solution, a fixing device may be provided on the carrierpart 2, which fixing device makes it possible to better fix the sensor 1on the finger or toe. By way of example, such a fixing device may beconfigured as a latching or clip closure which fixes the carrier legs12, 13 relative to one another at the respective opening width. It islikewise possible to attach a Velcro closure to one of the carrier legs12, 13, which Velcro closure is wound around the finger or toe after thesensor 1 has been pushed on.

By virtue of the simple design of the sensor 1 according to theinvention, the latter may be configured for example as a disposablesensor. Suitable materials for the carrier part 2 are then relativelyinexpensive polymers, such as crayton or TPE (santoprene). Materialsthat are suitable for the spring part are then comparatively inexpensivepolymers, such as polystyrene, ABS or SAN. Inexpensive components canthen be used for the optoelectronic elements, that is to say transmitterunit 5, receiver unit 6 and plug 9.

As an alternative, it is also possible to configure the sensor 1according to the invention as a reusable multiway sensor. For themanufacture of the carrier part 2, higher-quality polymers such assilicone or polyurethane are then suitable. The spring part 3 may thenlikewise be manufactured from high-quality polymers, such aspolyoxymethylene or polyamide. High-quality components which aresuitable for multiple use are then used for the optoelectronic elements.

In summary, the present invention can be characterized in that thesensor 1 is composed of a relatively flexible carrier part 2, which isused to retain the transmitter unit 5 and the receiver unit 6, and of arelatively rigid spring part 3, which is arranged on the outside of thecarrier part 2 and presses the latter against the finger or toe formeasurement purposes. The U-shaped or C-shaped or clip-shapedconfiguration of the carrier part 2 and of the spring part 3 allows thesensor 1 to be used on fingers or toes of varying size, so that one andthe same sensor 1 can always be used for different patient groups. As aresult, the number of sensors manufactured may be increased and hencethe price thereof will be reduced. The spring part 3 can be designedwith a relatively low complexity such that the sensor 1 has a springcharacteristic which always generates suitable application forces forfingers or toes of different size.

LIST OF REFERENCES

-   1 sensor-   2 carrier part-   3 spring part-   4 signal transmission unit-   5 transmitter unit-   6 receiver unit-   7 first cable-   8 second cable-   9 plug-   10 collective cable-   11 common cable-   12 first carrier leg-   13 second carrier leg-   14 carrier base-   15 first spring leg-   16 second spring leg-   17 spring base-   18 inner side of 12-   19 inner side of 13-   20 side cheek of 12-   21 side cheek of 13-   22 central zone of 12-   23 central zone of 13-   24 groove-   25 outer side of 12-   26 outer side of 14-   27 outer side of 13-   28 first recess-   29 second recess-   30 cable channel-   31 further cable channel-   32 end section of 11-   33 transmission opening in 28-   34 receiving opening in 29-   35 receiving contour of 2-   36 first spring zone-   37 second spring zone-   38 region-   39 support section-   39 a first support section-   39 b second support section-   39 c third support section-   40 transition between 16 and 17-   41 step-   42 end section of 15-   43 start section of 15-   44 flattening-   45 stop-   46 ramp-   47 hollow-   48 fixing tape

1. A medical sensor for measuring pulse blood tissue and/or skin parameters using electromagnetic waves for transmission, comprising: a clip-like carrier part for pushing onto a patient's finger or toe from the front; a first carrier leg that carries at least one transmitting element and bears with its inner side against the finger or toe during a measurement operation; a second carrier leg that carries at least one receiving element and bears with its inner side against the finger or toe, opposite the first carrier leg, during the measurement operation; a carrier base that connects the two carrier legs to one another in the region of a tip of the finger or toe; a clip-like spring part having two spring legs and a spring base that connects the spring legs, wherein the spring part is arranged on the outside of the carrier part such that the first spring leg bears against an outer side of the first carrier leg and the second spring leg bears against an outer side of the second carrier leg; wherein the carrier art is made of a more flexible material than the spring part; wherein the spring legs prestress the carrier legs toward one another; wherein the first spring leg has a start section that adjoins the spring base and an end section that is remote from the spring base; and wherein the end section is more flexible than the start section.
 2. A sensor as claimed in claim 1, wherein the carrier part is made in one piece and/or the spring part is made in one piece.
 3. A sensor as claimed in claim 1, wherein the spring part has at least one spring zone which connects together two support sections that adjoin it, and the support sections are more rigid than the spring zone.
 4. A sensor as claimed in claim 3, wherein the spring part has at least two spring zones with different spring elasticities.
 5. A sensor as claimed in claim 4, wherein the support sections which adjoin the more flexible spring zone form a stop which restricts the bending deformation in this spring zone to a predefined extent during widening of the carrier legs.
 6. A sensor as claimed in claim 3, wherein a spring zone is made at a transition between the second spring leg and the spring base and/or a spring zone is made approximately in the middle of the spring base.
 7. A sensor as claimed in claim 3, wherein the spring part has a first spring zone which is made at a transition between the second spring leg and the spring base, the spring part has a second spring zone which is made approximately in the middle of the spring base, and the second spring zone is more rigid than the first spring zone.
 8. A sensor as claimed in claim 1, wherein the carrier base is designed as a hollow configured to receive a fingernail or toenail during the measurement operation.
 9. A sensor as claimed in claim 1, wherein the inner sides of the carrier legs are curved in a concave manner transversely to a push-on direction, along which the sensor is pushed from an initial position onto a finger or toe, on each carrier leg side cheeks project beyond a center zone, and the spring part prestresses the carrier legs toward one another in such a way that the carrier legs bear against one another at their side cheeks prior to the sensor being pushed onto the finger or toe.
 10. A sensor as claimed in claim 1, wherein on the outside of the carrier part there is a groove which extends from the outer side of the first carrier leg via an outer side of the carrier base to the outer side of the second carrier leg, in which the at least one transmitting element and the at least one receiving element are arranged and in which connection cables for the transmitting element and the receiving element are laid, and in which the spring part closes the groove from outside.
 11. A sensor as claimed in claim 1, wherein the carrier part has a fixing device which allows fixing of the sensor on the finger or toe after the sensor has been pushed onto the finger or toe.
 12. A sensor as claimed in claim 1, wherein the end section is more rigid than the second spring zone.
 13. A sensor as claimed in claim 1, wherein the end section is connected to the start section in a region that is approximately central with respect to the second spring leg.
 14. A medical sensor comprising: a carrier part formed by two legs joined by a base and defining a region therein for placement of a patient part; and a spring part formed by two legs joined by a base, wherein the spring part legs apply force to carrier part legs to secure the medical sensor on the patient part, wherein the spring part further comprises at least two spring zones having different spring elasticities; and wherein a first spring zone is formed by a material contraction to have a greater elasticity than a second spring zone.
 15. The medical sensor of claim 14, wherein the first spring zone is made at a transition between one of the spring part legs and the spring part base and the second spring zone is made approximately in the middle of the spring part base.
 16. The medical sensor of claim 15, wherein the first spring zone further comprises a stop beyond which the first spring zone cannot flex.
 17. The medical sensor of claim 14, wherein the second spring zone is flattened to have a lesser elasticity than the first spring zone, and wherein the spring part flexes at the first spring zone until a spring stop is reached, thereafter the spring part flexes at the second spring zone.
 18. A medical sensor comprising: a carrier part defining a region therein for placement of a patient part; and a spring part that fits over the carrier part and applies force to secure the carrier part on the patient part; wherein the spring part includes at least two spring zones having different spring elasticities and a spring stop, wherein the spring part flexes at a first spring zone until the spring stop is reached, thereafter the spring part flexes at a second spring zone.
 19. The medical sensor of claim 18, wherein the first spring zone is made at a transition between a spring part leg and a spring part base and the second spring zone is made approximately in the middle of the spring part base.
 20. The medical sensor of claim 18, wherein the carrier part further comprises two legs joined by a base, a transmitter located on a first of said legs, and a receiver located on a second of said legs. 